Replenishable liquid storage tank including backpressure application member, and image-forming apparatus provided with the same

ABSTRACT

A replenishing-type liquid storage tank includes a tank body, and a backpressure application member. Liquid is replenishable in the tank body and the tank body is configured to store the liquid therein. The backpressure application member is accommodated in the tank body to apply backpressure to the liquid stored in the tank body. The backpressure application member has a lower end positioned at a height equal to or lower than a liquid level of a minimum amount of liquid required to be stored in the tank body for enabling the backpressure application member to apply backpressure to the liquid stored in the tank body.

CROSS REFERENCE TO RELATED APPLICATION

This Application is a Division of application Ser. No. 16/805,264 filedFeb. 28, 2020, which claims priority from Japanese Patent ApplicationNos. 2019-066702 filed Mar. 29, 2019 and 2019-066703 filed Mar. 29,2019. The entire contents of the priority applications are incorporatedherein by reference.

TECHNICAL FIELD

The present disclosure relates to a liquid storage tank to which liquidis replenishable, and to an image-forming device provided with theliquid storage tank.

BACKGROUND

There is a well-known ink jet printer provided with a liquid storagetank for storing a liquid such as ink, and configured to consume theliquid stored in the tank. As such a liquid storage tank, arefillable-type liquid storage tank is known in the art. For example,Japanese Patent Application Publication No. 2018-161851 discloses areplenishable liquid storage tank into which liquid is suitablyreplenishable.

In such conventional ink jet printers, application of backpressure,i.e., negative pressure, to the ink stored in the liquid storage tank isrequired to form a meniscus of ink at a tip end portion of a nozzlewhich does not perform ink ejection in order to prevent the ink frombeing leaked through the nozzle. Conventionally, a differential pressureregulating valve is available as means for applying backpressure to theink stored in the liquid storage tank. The differential pressureregulating valve is configured to be opened and closed in accordancewith the pressure difference between upstream side and downstream sideof the valve. Opening and closing of the valve can control backpressureapplied to the ink.

SUMMARY

However, the differential pressure regulating valve is positioned midwaybetween the liquid storage tank and the nozzle in a liquid supply systemfor supplying the ink from the liquid storage tank and the nozzle.Hence, the ink supply system inevitably becomes bulky.

Instead of the differential pressure regulating valve, an ink absorberfor absorbing ink may be provided in a liquid storage tank for applyingbackpressure to the ink in the liquid storage tank. In a case where suchbackpressure application is performed by means of an ink absorber, asufficient backpressure may not be applied to the ink if a sufficientamount of ink is not absorbed in the absorber due to decrease in theamount of ink left in the liquid storage tank.

In view of the foregoing, it is an object of the present disclosure toprovide a replenishable liquid storage tank and an image-forming deviceprovided with the tank capable of applying a sufficient backpressure toliquid stored in the tank, yet obviating increase in size of the entireliquid supply system.

Another object of the disclosure is to provide a replenishable liquidstorage tank provided with a liquid absorber as a backpressureapplication means and an image-forming apparatus including the tankcapable of applying sufficient backpressure to the liquid stored in thetank, irrespective of decrease in residual amount of liquid in the tank.

In order to attain the above and other objects, according to one aspect,the disclosure provides a replenishing-type liquid storage tankincluding a tank body, a backpressure application member, and an upperlimit indicator. Liquid is replenishable in the tank body and the tankbody is configured to store the liquid therein. The backpressureapplication member is made from a material capable of absorbing liquidand is accommodated in the tank body to apply backpres sure to theliquid stored in the tank body. The upper limit indicator is set in thetank body. The upper limit indicator is indicative of a liquid level ofa maximum tolerable amount of the liquid that can be stored in the tankbody. The backpressure application member has a portion positionedhigher than the upper limit indicator.

According to another aspect, the disclosure provides an image-formingapparatus including: the above replenishing-type liquid storage tank;and a recording head configured to form an image on an image recordingmedium with the liquid supplied from the replenishing-type liquidstorage tank.

According to still another aspect, the disclosure provides areplenishing-type liquid storage tank including a tank body, abackpressure application member, and a functional lower limit indicator.Liquid is replenishable in the tank body and the tank body is configuredto store the liquid therein. The backpressure application member is madefrom a material capable of absorbing liquid and is accommodated in thetank body to apply backpressure to the liquid stored in the tank body.The functional lower limit indicator is set in the tank body. Thefunctional lower limit indicator is indicative of a liquid level of aminimum amount of liquid required to be stored in the tank body forenabling the backpressure application member to apply backpressure tothe liquid stored in the tank body. The backpressure application memberhas a lower end positioned at a height equal to or lower than thefunctional lower limit indicator.

According to still another aspect, the disclosure provides animage-forming apparatus including: the above replenishing-type liquidstorage tank according to the still another aspect; and a recording headconfigured to form an image on an image recording medium with the liquidsupplied from the replenishing-type liquid storage tank.

BRIEF DESCRIPTION OF THE DRAWINGS

The particular features and advantages of the disclosure as well asother objects will become apparent from the following description takenin connection with the accompanying drawings, in which:

FIG. 1 is a schematic vertical cross-sectional view of areplenishing-type liquid storage tank according to a first embodiment;

FIG. 2 is a schematic view illustrating an image-forming apparatusincluding the replenishing-type liquid storage tank according to thefirst embodiment;

FIG. 3 is a schematic view illustrating various patterns of backpressureapplication members that can be used in the replenishing-type liquidstorage tank according to the first embodiment;

FIG. 4 is a schematic view illustrating a portion of a replenishing-typeliquid storage tank according to a first modification to the firstembodiment;

FIG. 5 is a schematic view illustrating a portion of a replenishing-typeliquid storage tank according to a second modification to the firstembodiment;

FIG. 6 is a schematic vertical cross-sectional view illustrating areplenishing-type liquid storage tank according to a third modificationto the first embodiment;

FIG. 7 is a schematic vertical cross-sectional view illustrating areplenishing-type liquid storage tank according to a fourth modificationto the first embodiment;

FIG. 8 is a schematic vertical cross-sectional view of areplenishing-type liquid storage tank according to a second embodiment;

FIG. 9 is a schematic vertical cross-sectional view illustrating areplenishing-type liquid storage tank according to a first modificationto the second embodiment;

FIG. 10 is a schematic vertical cross-sectional view illustrating areplenishing- type liquid storage tank according to a secondmodification to the second embodiment;

FIG. 11 is a schematic vertical cross-sectional view illustrating areplenishing- type liquid storage tank according to a third modificationto the second embodiment;

FIG. 12 is a schematic vertical cross-sectional view illustrating areplenishing- type liquid storage tank according to a fourthmodification to the second embodiment;

FIG. 13 is a schematic view illustrating a portion of areplenishing-type liquid storage tank according to a fifth modificationto the second embodiment;

FIG. 14 is a schematic view illustrating a portion of areplenishing-type liquid storage tank according to a sixth modificationto the second embodiment;

FIG. 15 is a schematic vertical cross-sectional view illustrating areplenishing- type liquid storage tank according to a seventhmodification to the second embodiment; and

FIG. 16 is a schematic vertical cross-sectional view illustrating areplenishing- type liquid storage tank according to an eightmodification to the second embodiment.

DETAILED DESCRIPTION

First, an ink storage tank 1 as an example of a replenishing-type liquidstorage tank according to a first embodiment of the disclosure will bedescribed with reference to FIG. 1. The ink storage tank 1 is providedin an image-forming apparatus 100 (see FIG. 2). The ink storage tank 1illustrated in FIG. 1 is in an operable posture thereof.

The tank 1 includes a tank body 2 constituting an outer shell of thetank 1, and a backpressure application member 3 positioned in aninterior of the tank body 2. A partitioning wall 4 is provided in theinterior of the tank body 2 to divide an internal space of the tank body2 into an ink storage portion 5 and an absorber accommodating portion 6for accommodating therein the backpressure application member 3. The inkstorage portion 5 provides a space for storing ink therein.

The tank body 2 includes a flat bottom wall 2 b, side walls 2 c, and atop wall 2 a. The side walls 2 c include: a first side wall 2 c 1extending upward from one end portion of the bottom wall 2 b ; and asecond side wall 2 c 2 extending upward from another end portion of thebottom wall 2 b. The top wall 2 a extends to connect an upper endportion of the first side wall 2 c 1 to an upper end portion of thesecond side wall 2 c 2.

More specifically, the first side wall 2 c 1 functions as a wallconstituting the ink storage portion 5, and the second side wall 2 c 2functions as a wall constituting the absorber accommodating portion 6.The second side wall 2 c 2 has a length in an upward/downward directiongreater than that of the first side wall 2 c 1. The top wall 2 a the topwall 2 a is in a stepped form and includes: a lower wall section 2 a 2and a higher wall section 2 a 1 positioned higher than the lower wallsection 2 a 2. The lower wall section 2 a 2 functions as a wallconstituting the ink storage portion 5. The higher wall section 2 a 1functions as a wall constituting the absorber accommodating portion 6.That is, an upper end of the absorber accommodating portion 6 is higherthan an upper end of the ink storage portion 5. In other words, theabsorber accommodating portion 6 has a length in the upward/downwarddirection greater than that of the ink storage portion 5.

The partitioning wall 4 extends linearly downward from the top wall 2 aat a boundary between the ink storage portion 5 and the absorberaccommodating portion 6. The partitioning wall 4 has a lower endpositioned to be spaced away from the bottom wall 2 b to provide a gap 4a therebetween. Hence, in the interior of the tank body 2, a lowerportion of the ink storage portion 5 and a lower portion of the absorberaccommodating portion 6 are in communication with each other through thegap 4 a. The partitioning wall 4 is made from a liquid impermeablematerial.

An auxiliary absorber 7 is also positioned in the ink storage tank 1.The auxiliary absorber 7 extends horizontally over the ink storageportion 5 and the absorber accommodating portion 6 through the gap 4 a.The auxiliary absorber 7 is positioned below the backpressureapplication member 3 and in contact with the backpressure applicationmember 3 from below. The auxiliary absorber 7 is made from a liquidabsorbing member such as an artificial sponge, a natural sponge, and abundle of capillary tubes, and serves to help ink move from the inkstorage portion 5 to the absorber accommodating portion 6.

Further, the ink storage tank 1 includes an ink inlet port 8. Ink isreplenishable into the tank body 2 through the ink inlet port 8. Inother words, the ink storage tank 1 is configured as a refillable inkstorage tank into which ink can be refilled from an outside.

The ink inlet port 8 is provided at the lower wall section 2 a 2 of thetop wall 2 a. The ink inlet port 8 extends throughout a thickness of thelower wall section 2 a 2 in the upward/downward direction, and has alower end positioned below the lower wall section 2 a 2. That is, thelower end of the ink inlet port 8 is positioned in the interior of thetank body 2. Specifically, the ink inlet port 8 has a tubular shapeprotruding into the interior of the tank body 2. Further, the ink inletport 8 has an upper end portion protruding upward from the lower wallsection 2 a 2. A cap 8 a is attachable to and detachable from the upperend portion of the ink inlet port 8 for sealing the ink inlet port 8.

An air communication port 9 is formed in the lower wall section 2 a 2 ofthe top wall 2 a. The air communication port 9 provides aircommunication between the interior and an exterior of the tank body 2.

An upper limit indicator UL is set in the ink storage tank 1. The upperlimit indicator UL is a line indicating a maximum level of inkcorresponding to a maximum tolerable amount of ink that can be stored inthe tank body 2. In the present embodiment, the upper limit indicator ULis in a form of a rib 2L (a physically visible structure) protrudingfrom the first side wall 2 c 1 to extend linearly in a horizontaldirection therefrom. With this structure, a user can visually recognizethe height of the rib 2L as being the upper limit of the ink (i.e., theheight of the upper limit indicator UL).

Incidentally, instead of the rib 2L, a linear groove extending in thehorizontal direction may be formed in the first side wall 2 c 1 as theupper limit indicator UL. Alternatively, a label directly printed on thefirst side wall 2 c 1 or a seal adhered to the first side wall 2 c 1 mayalso be available as the upper limit indicator UL. Still alternatively,a plurality of protruding dots or a plurality of dimpled dots thosearrayed in line in the horizontal direction may be formed in the firstside wall 2 c 1 as the upper limit indicator UL. In any case, the upperlimit indicator UL should be positioned higher than a center of the tankbody 2 in the upward/downward direction.

Further, the upper limit indicator UL is at a height equal to or lowerthan the lower end of the ink inlet port 8.

Incidentally, the tank body 2 has a window at a position coincident withor overlapped with the upper limit indicator UL. The window is formed ofa transparent or translucent material so that the level of ink in thetank body 2 can be visually recognized through the window.Alternatively, the tank body 2 in its entirety may be made from atransparent or translucent material.

The gap 4 a provided by the partitioning wall 4 and the bottom wall 2 bis positioned lower than the rib 2L indicative of the upper limitindicator UL. In other words, the ink storage portion 5 and the absorberaccommodating portion 6 are in communication with each other through thegap 4 a positioned below the upper limit indicator UL (rib 2L).

The ink storage tank 1 is further provided with an ink outlet port 10for discharging the ink stored in the tank body 2 to the outsidethereof. The ink outlet port 10 is provided in the bottom wall 2 b.Specifically, the ink outlet port 10 is formed in a portion of thebottom wall 2 b, the portion constituting the absorber accommodatingportion 6. Hence, the ink in the ink storage tank 1 can be supplied to arecording head 11 through the ink outlet port 10. Incidentally, therecording head 11 includes a plurality of nozzles through which ink isconfigured to be ejected to an image-forming medium such as a sheet toform an image on the medium.

Next, the backpressure application member 3 will be described in detail.The backpressure application member 3 is made from an absorbing materialcapable of absorbing ink. An artificial sponge, a natural sponge, abundle of capillary tubes and other members capable of absorbing ink areavailable as the absorbing member. The backpressure application member 3is configured to absorb, through the gap 4 a, ink replenished into thetank body 2 through the ink inlet port 8. That is, the ink is initiallyabsorbed into the lower portion of the backpressure application member3, and then the absorbed ink is permeated upward in the backpressureapplication member 3.

Further, at least a part of the backpressure application member 3 (i.e.,an upper portion of the backpressure application member 3 in theembodiment) is positioned higher than the upper limit indicator UL.Further, an upper end of the backpressure application member 3 ispositioned above the lower end of the ink inlet port 8. Furthermore, theupper end of the backpressure application member 3 is positioned abovethe lower wall section 2 a 2 of the top wall 2 a. Still further, theupper end of the backpressure application member 3 is positioned abovethe upper end portion of the ink inlet port 8.

In the interior of the tank body 2, the ink storage portion 5 and thepartitioning wall 4 are positioned between the backpressure applicationmember 3 and the ink inlet port 8. Hence, the ink inlet port 8 isprovided so as not to make direct contact with the backpressureapplication member 3.

As illustrated in FIG. 2, the ink storage tank 1 is provided in theimage-forming apparatus 100, such as an ink jet printer. Theimage-forming apparatus 100 is a so-called on-carriage type printer inwhich the ink storage tank 1 is mounted on a carriage 101 reciprocallymovable over an image-forming medium during image formation.Incidentally, the image-forming device 100 may be an off-carriage typeprinter in which the ink storage tank 1 is provided on a portion otherthan the carriage. Alternatively, the image-forming apparatus 100 may bea line printer in which a plurality of stationary image forming unitsare arrayed in line. Alternatively, the image-forming device 100 may bea type in which the ink storage tank 1 is detachable from and attachableto the apparatus, or may be a type where the ink storage tank 1 isfixedly secured to the apparatus. Further, the image-forming apparatus100 may form images with liquid other than ink.

In the ink storage tank 1 according to the first embodiment, at least aportion of the backpressure application member 3, i.e., at least theupper portion of the backpressure application member 3 is positionedabove the upper limit indicator UL. Therefore, the ink absorbed in thebackpressure application member 3 is not likely to spread up to theupper portion, and accordingly, the backpressure application member 3can have a portion where the ink is not absorbed. This means that inkabsorbing function can still be exhibited in the backpressureapplication member 3 even if ink is refilled into the tank body 2 up tothe level of the upper limit indicator UL. Consequently, sufficientbackpressure can be securely and stably applied to the ink in the tankbody 2.

Further, the backpressure application member 3 made from an inkabsorbing material is remarkably simple in construction in comparisonwith the conventional differential pressure regulating valve. Therefore,increase in size of the ink supply system from the ink storage tank 1 tothe nozzles of the recording head 11 can be obviated.

Further, also conventionally well-known is a backpressure generatingstructure by way of difference in height between an ink storage tank andan image-forming unit, i.e., a backpressure application structureutilizing water head difference. According to the structure utilizingthe water head difference, the ink supply system becomes bulky because acertain level difference is required between the ink storage tank andthe image-forming unit.

On the other hand, in the ink storage tank 1 according to the firstembodiment, the backpressure application structure does not utilizewater head difference, but employs the simple backpressure applicationmember 3 made from an absorbing member. Hence, the ink storage tank 1according to the embodiment is on a basis of a technology quitedifferent from the conventional backpressure application structureutilizing water head difference.

Further, according to the ink storage tank 1, the upper end of thebackpressure application member 3 is positioned higher than the lowerend of the ink inlet port 8 positioned above the upper limit indicatorUL. Hence, even if ink is excessively replenished in the tank body 2beyond the upper limit indicator UL, a non-ink absorbing portion of thebackpressure application member 3 is still likely to exist, andaccordingly, backpressure can be stably and securely applied to the ink.

Further, according to the ink storage tank 1, the upper end of thebackpressure application member 3 is positioned higher than the lowerwall section 2 a 2 of the top wall 2 a positioned above the lower end ofthe ink inlet port 8. Hence, even if ink is excessively replenished inthe tank body 2 exceeding the upper limit indicator UL, a non-inkabsorbing portion of the backpressure application member 3 may stillexist, and accordingly, backpressure can be stably and securely appliedto the ink.

Further, according to the ink storage tank 1, the upper end of thebackpressure application member 3 is positioned higher than the upperend portion of the ink inlet port 8 positioned above the lower wallsection 2 a 2. Hence, even if the ink is excessively replenished in thetank body 2 exceeding the upper limit indicator UL, a non-ink absorbingportion of the backpressure application member 3 still exists, andaccordingly, backpressure can be stably and securely applied to the ink.

Further, according to the ink storage tank 1, the interior of the tankbody 2 to which ink is replenished is divided into the ink storageportion 5 and the absorber accommodating portion 6 by the partitioningwall 4. With this structure, the partitioning wall 4 can restrain aircontained in the ink storage portion 5 from directly contacting with thebackpressure application member 3 accommodated in the absorberaccommodating portion 6.

Further, in the tank body 2, the ink storage portion 5 and the absorberaccommodating portion 6 are in communication with each other through thegap 4 a formed by the partitioning wall 4. Therefore, the ink is allowedto move smoothly from the ink storage portion 5 to the absorberaccommodating portion 6 despite the provision of the partitioning wall4.

Further, according to the ink storage tank 1, the ink inlet port 8 ispositioned at the top wall 2 a, rather than at the side wall 2 c. Withthis structure, the ink can be replenished into the tank body 2 fromabove, thereby facilitating ink replenishing labor. However, the inkinlet port 8 may be positioned at the side wall 2 c. In the latter case,the ink inlet port 8 may be formed to have a slanted portion whose openend faces upward.

Various modifications are conceivable to the ink storage tank 1 of thefirst embodiment. Hereinafter, several modifications to the firstembodiment will be described with reference to FIGS. 3 through 7. Likeparts and components are designated by the same reference numerals asthose of the first embodiment to avoid duplicating description.

FIG. 3 illustrates various modifications to the backpressure applicationmember 3. Each of backpressure application members 3A, 3B and 3C shownin FIG. 3 has at least a portion positioned higher than the upper limitindicator UL. That is, as in the backpressure application members 3A-3C,the backpressure application member 3 may have various shapes, providedthat the upper end portion thereof is positioned above the upper limitindicator UL.

FIG. 4 depicts a replenishing-type ink storage tank according to a firstmodification to the first embodiment. This ink storage tank includes anink inlet port 108 whose lower end does not protrude into an interior ofthe tank body 2 from the top wall 2 a. In this case, the upper endportion of the backpressure application member 3 may be positionedhigher than the lower end of the ink inlet port 108.

FIG. 5 illustrates a replenishing-type ink storage tank according to asecond modification to the first embodiment. This ink storage tankincludes a cap 208 a, instead of the cap 8 a of the first embodiment.The cap 208 a includes a sleeve portion 208 a 1 insertable into the inkinlet port 8. The sleeve portion 208 a 1 has a lower end positionedlower than the lower end of the ink inlet port 8. Further, the upper endof the backpressure application member 3 is positioned higher than thelower end of the sleeve portion 208 a 1.

FIG. 6 illustrates a replenishing-type ink storage tank 301 according toa third modification to the first embodiment. In this ink storage tank301, two air communication ports 309 are formed one each in a higherwall section 302 a 1 of a top wall 302 a of a tank body 302, and a lowerwall section 302 a 2 of the top wall 302 a. As a further modification,only the air communication port 309 may be provided at the higher wallsection 302 a 1, while the air communication port 309 on the lower wallsection 302 a 2 may be omitted.

A replenishing-type ink storage tank 401 according to a fourthmodification is illustrated in FIG. 7. In a tank body 402 of the inkstorage tank 401, the partitioning wall 4 is not provided, and abackpressure application member 403 is accommodated not only in theabsorber accommodating portion 6 but also in the ink storage portion 5.Hence, the backpressure application member 403 has a steppedconfiguration having a higher level end 403 a 1 and a lower level end403 a 2 lower than the higher level end 403 a 1. The upper limitindicator UL is positioned, at least, higher than the lower level end403 a 2.

Incidentally, the ink inlet port 8 is positioned to be separated fromthe lower level end 403 a 2, so that the ink inlet port 8 does not makecontact with the backpressure application member 403. Further, theauxiliary absorber 7 can be omitted. Further, the air communication port9 may be formed in the higher wall section 2 a 1, instead of the lowerwall section 2 a 2.

Incidentally, in the ink storage tank 1 including the partitioning wall4, the air communication port 9 is preferably formed in the lower wallsection 2 a 2 rather than the higher wall section 2 a 1. Further, in theink storage tank 401 not having the partitioning wall 4, the aircommunication port 9 is preferably formed in the higher wall section 2 a1 rather than the lower wall section 2 a 2. The ink storage tank 1including the partitioning wall 4 and formed with the air communicationport 9 in the lower wall section 2 a 2 is most preferable.

Next, a replenishing-type ink storage tank 501 according to a secondembodiment will be described with reference to FIG. 8. Like parts andcomponents are designated by the same reference numerals as those of thefirst embodiment to avoid duplicating description.

The ink storage tank 501 of the second embodiment is mounted on thecarriage 101 of the image-forming apparatus 100 (see FIG. 2), in placeof the ink storage tank 1 of the first embodiment.

As in the ink storage tank 1 of the first embodiment, the backpressureapplication member 3 and the auxiliary absorber 7 are accommodated in atank body 502 of the ink storage tank 501 of the second embodiment. Asin the first embodiment, the auxiliary absorber 7 is positioned belowthe backpressure application member 3 to be in contact therewith; andthe auxiliary absorber 7 extends across the ink storage portion 5 andthe absorber accommodating portion 6 through the gap 4 a.

Referring to FIG. 8, a functional lower limit indicator ML1 is set inthe tank body 502 of the ink storage tank 501. The functional lowerlimit indicator ML1 is a line indicating a minimum level of inkcorresponding to a minimum tolerable amount of ink that can be stored inthe tank body 502 in order to maintain backpressure application functionof the backpressure application member 3. The functional lower limitindicator ML1 is positioned lower than the center of the tank body 502in the upward/downward direction. Further, the functional lower limitindicator ML1 is positioned higher than the bottom wall 2 b of the tankbody 502.

In the ink storage tank 501 of the second embodiment, at least a part ofthe backpressure application member 3 (lower end portion thereof) is ata height equal to or lower than the functional lower limit indicatorML1. More specifically, in the tank body 502, the functional lower limitindicator ML1 is positioned higher than the auxiliary absorber 7 andlower than the lower end of the partitioning wall 4 in theupward/downward direction, as illustrated in FIG. 8.

The lower end of the backpressure application member 3 is positioned ata height equal to or lower than a visual lower limit indicator ML2. Thevisual lower limit indicator ML2 is a line indicating a lowermost liquidlevel that allows user's visual inspection of the amount of ink storedin the tank body 502. The visual lower limit indicator ML2 is in a formof a physically visible rib 502L protruding from the first side wall 2 c1 to extend in a horizontal direction. A user can visually recognize theheight of the rib 502L as the visual lower limit indicator ML2 (thelower limit for user's visual inspection to the ink).

The ink storage portion 5 has a lower space lower than the rib 502Lindicative of the visual lower limit indicator ML2, and the absorberaccommodating portion 6 has a lower space lower than the rib 502L. Thelower space of the ink storage portion 5 and the lower space of theabsorber accommodating portion 6 are in communication with each otherthrough the gap 4 a between the partitioning wall 4 and the bottom wall2 b.

Incidentally, instead of the rib 502L, a linear groove extending in thehorizontal direction may be formed in the first side wall 2 c 1 as theindicator of the visual lower limit indicator ML2. Alternatively, alabel directly printed on the side wall 2 c or a seal adhered to thefirst side wall 2 c 1 may also be available as the visual lower limitindicator ML2. Further alternatively, a plurality of protruding dots ora plurality of dimpled dots those arrayed in line in the horizontaldirection may be formed in the first side wall 2 c 1 as the visual lowerlimit indicator ML2. The visual lower limit indicator ML2 may be invarious forms, provided that the user can visually recognize a level ofa prescribed amount of ink in the tank body 502 from the visual lowerlimit indicator ML2. In any case, the visual lower limit indicator ML2is positioned higher than the functional lower limit indicator ML1. Inother words, the functional lower limit indicator ML1 is positionedlower than the visual lower limit indicator ML2.

Incidentally, the tank body 502 has a window at a position coincidentwith or overlapped with the visual lower limit indicator ML2. The windowis formed of transparent or translucent material so that the level ofink can be visually recognized through the window. Alternatively, thetank body 502 in its entirety may be made from transparent ortranslucent material.

Further, the lower end of the backpressure application member 3 ispositioned at a height equal to or lower than a control lower limitindicator ML3. The control lower limit indicator ML3 is a line to bereferred to by a computer to detect whether the residual amount of inkin the tank body 502 is minimum based on an amount of the ink ejectedthrough the recording head 11. The control lower limit indicator ML3linearly extends in the horizontal direction on the first side wall 2 c1. The control lower limit indicator ML3 is positioned at a heighthigher than the functional lower limit indicator ML1 and lower than thevisual lower limit indicator ML2. That is, the control lower limitindicator ML3 is positioned between the functional lower limit indicatorML1 and the visual lower limit indicator ML2. The functional lower limitindicator ML1 is lower than the control lower limit indicator ML3.

Incidentally, the control lower limit indicator ML3 may be higher thanthe visual lower limit indicator ML2. Further, a controller (notillustrated) controlling overall operations of the image-formingapparatus 100 may be available as the computer configured to refer tothe control lower limit indicator ML3. A microcomputer is a maincomponent of the controller, and is configured to count the amount ofink ejected from the nozzles of the recording head 11, and determine, ona basis of the counted value, whether the residual amount of ink in thetank body 502 is decreased to the level corresponding to the controllower limit indicator ML3.

In the ink storage tank 501 according to the second embodiment, at leasta portion (lower end portion) of the backpressure application member 3for applying backpressure to the ink stored in the tank body 502 is atthe height equal to or lower than the functional lower limit indicatorML1. With this structure, even if the level of the residual inkremaining in the tank body 502 is decreased to a level corresponding tothe functional lower limit indicator ML1, the lower end portion of thebackpressure application member 3 can be kept immersed in the ink, sothat the backpressure application member 3 can still absorb ink.Consequently, sufficient backpressure can be applied to the inkremaining in the tank body 502 even if the residual amount of inktherein is decreased.

Further, in the ink storage tank 501 according to the second embodiment,the functional lower limit indicator ML1 is positioned lower than thevisual lower limit indicator ML2. With this structure, the user canvisually recognize the decrease in the residual amount of ink in thetank body 502 before the residual amount of ink is lowered to the levelcorresponding to the functional lower limit indicator ML1. In otherwords, the decrease in the residual amount of ink to the level of thevisual lower limit indicator ML2 can prompt the user to replenish inkinto the tank body 502 at a suitable timing earlier than otherwise.Consequently, insufficient application of backpressure to the ink can berestrained.

Further, in the ink storage tank 501 according to the second embodiment,the functional lower limit indicator ML1 is positioned below the controllower limit indicator ML3. With this structure, the controller of theimage-forming apparatus 100 can give a warning to the user to notify thedecrease in residual amount of ink in the tank body 502 before theresidual amount of ink is decreased to the level of the functional lowerlimit indicator ML1. Accordingly, the user can be prompted to performreplenishment of ink to the tank body 502 at an early stage, and hence,insufficient application of backpressure to the ink can be restrained.

Further, in the ink storage tank 501 according to the second embodiment,the functional lower limit indicator ML1 is positioned above an upperend of the ink outlet port 10, and higher than the lower end of thebackpressure application member 3. Therefore, even if the residualamount of ink in the tank body 502 is decreased to the level of thefunctional lower limit indicator ML1, the ink in the tank body 502 isensured to flow out of the ink outlet port 10 through at least one ofthe backpressure application member 3 and the auxiliary absorber 7.

Incidentally, if the functional lower limit indicator ML1 is positionedbelow the upper end of the ink outlet port 10, air is likely to beintroduced directly into the ink outlet port 10, which may disable thenozzles of the recording head 11 for ejecting ink to possibly causedefective ink ejection. The ink storage tank 501 according to the secondembodiment can avoid occurrence of such defective ink ejection.

Various modifications are also conceivable to the ink storage tank 501of the second embodiment. Hereinafter, several modifications to thesecond embodiment will be described with reference to FIGS. 9 through16.

FIG. 9 illustrates a replenishing-type ink storage tank 601 according toa first modification to the second embodiment. In the ink storage tank601, the functional lower limit indicator ML1 is set at a height equalto or higher than the lower end of the partitioning wall 4. With thisstructure, even in a state where the residual amount of ink in a tankbody 602 is decreased to the level of the functional lower limitindicator ML1, the gap 4 a (functioning as an ink passage from the inkstorage portion 5 to the absorber accommodating portion 6) can be filledwith the ink. Hence, air is prevented from flowing from the ink storageportion 5 to the backpressure application member 3 accommodated in theabsorber accommodating portion 6.

In the ink storage tank 601, the functional lower limit indicator ML1 isstill lower than the visual lower limit indicator ML2 and the controllower limit indicator ML3, as in the second embodiment. A rib 602Lprovided on the first side wall 2 c 1 indicates the visual lower limitindicator ML2 of the tank body 602. The control lower limit indicatorML3 is positioned between the functional lower limit indicator ML1 andvisual lower limit indicator ML2.

FIG. 10 illustrates a replenishing-type ink storage tank 701 accordingto a second modification to the second embodiment. A tank body 702includes a bottom wall 702 b at which an ink outlet port 710 isprovided. An upper surface of the ink outlet port 710 (a surface facingan auxiliary absorber 707 disposed along the bottom wall 702 b ) has aportion in direct contact with the auxiliary absorber 707. That is, theauxiliary absorber 707 has a part directly exposed to one end (upperend) of the ink outlet port 710 through the bottom wall 702 b of thetank body 702.

FIG. 11 illustrates a replenishing-type ink storage tank 801 accordingto a third modification to the second embodiment. A tank body 802includes a bottom wall 802 b at which an ink outlet port 810 isprovided. An entire one end of the ink outlet port 810 facing anauxiliary absorber 807 (entire upper surface of the ink outlet port 810)is in direct contact with the auxiliary absorber 807. The auxiliaryabsorber 807 has a portion protruding downward through the bottom wall802 b.

Likewise, FIG. 12 illustrates a replenishing-type ink storage tank 901according to a fourth modification to the second embodiment. A tank body902 includes a bottom wall 902 b at which an ink outlet port 910 isprovided. An entire one end of the ink outlet port 910 facing anauxiliary absorber 907 (entire upper surface of the ink outlet port 910)is in direct contact with the auxiliary absorber 907. The auxiliaryabsorber 907 has a portion stepped upward, and the entire one end of theink outlet port 910 is in contact with the stepped portion of theauxiliary absorber 907.

The ink storage tanks 801 and 901 may be applied with variousmodifications, as long as the ink in the tank bodies 802, 902 passesthrough the auxiliary absorbers 807, 907 without fail before flowing outof the respective tank bodies 802, 902 through the respective ink outletports 810, 910.

Incidentally, in the ink storage tanks 801 and 901, the ink outlet port810, 910 may be arranged to face at least one of the backpressureapplication member 3 and the auxiliary absorber 807, 907. Specifically,in a case where the one end of the ink outlet port 810, 910 faces thebackpressure application member 3, an entirety or a part of the one end(upper surface) of the ink outlet port 810, 910 may be in direct contactwith the backpressure application member 3. In a case where the one endof the ink outlet port 810, 910 faces both of the auxiliary absorber807, 907 and the backpressure application member 3, a part or anentirety of the one end (upper surface) of the ink outlet port 810, 910may be in direct contact with each of the auxiliary absorber 807, 907and the backpressure application member 3. That is, the ink storagetanks 801 and 901 may be applied with various modifications, providedthat the liquid in the tank body 802, 902 is required to pass through atleast one of the backpressure application member 3 and the auxiliaryabsorber 807, 907 before flowing out of the tank body 802, 902 throughthe ink outlet port 810, 910, respectively.

FIGS. 13 and 14 illustrate replenishable ink storage tanks 1101, 1201according to fifth and sixth modifications to the second embodiment,respectively. In the ink storage tanks 1101 and 1201, ink outlet ports1110 and 1210 are out of contact with auxiliary absorbers 1107, 1207,respectively, provided that ink in respective tank bodies 1102 and 1202is ensured to pass through the corresponding auxiliary absorbers 1107and 1207 to flow out of the tank bodies 1102, 1202 through the inkoutlet ports 1110 and 1210.

Specifically, according to the ink storage tank 1101 illustrated in FIG.13, a rib 1110a protrudes into the interior of the tank body 1102 from abottom wall 1102 b thereof at a position upstream of the ink outlet port1110 in a flowing direction of the ink (downward in FIG. 13). Theauxiliary absorber 1107 is supported by the rib 1110a such that theauxiliary absorber 1107 is in contact with the rib 1110a. A closed space51 is defined by the rib 1110a and the auxiliary absorber 1107. Withthis structure, the ink in the tank body 1102 is required to passthrough the auxiliary absorber 1107 before flowing out of the tank body1102 through the ink outlet port 1110.

According to the ink storage tank 1201 illustrated in FIG. 14, a rib1210a protrudes into the interior of the tank body 1202 from a bottomwall 1202 b thereof at a position upstream of the ink outlet port 1210in the flowing direction of the ink (downward in FIG. 14). The auxiliaryabsorber 1207 has an end face in contact with an inner surface of thetank body 1202, such that a part of the auxiliary absorber 1207 isseparated from the rib 1210a. A closed space S2 is defined by the innersurface of the tank body 1202 and the auxiliary absorber 1207. With thisstructure, the ink in the tank body 1202 needs to pass through theauxiliary absorber 1207 before flowing out of the tank body 1202 throughthe ink outlet port 1210.

Incidentally, the ink outlet port 1210 may directly face thebackpressure application member 3 with a space therebetween, rather thanwith the auxiliary absorber 1207, provided that the backpressureapplication member 3 is in contact with the inner surface of the tankbody 1202 to define a closed space corresponding to the closed space S2with the inner surface of the tank body 1202.

In other words, one end of the ink outlet port 1210 facing at least oneof the backpressure application member 3 and the auxiliary absorber 1207(i.e., an upper end of the ink outlet port 1210) may be arranged to beseparated from the one of the backpressure application member 3 andauxiliary absorber 1207, provided that the one of the backpressureapplication member 3 and the auxiliary absorber 1207 is in contact withthe inner surface of the tank body 1202 to define a closed spacecorresponding to the closed space S2 with the inner surface of the tankbody 1202.

FIG. 15 illustrates a replenishing-type ink storage tank 1301 accordingto a seventh modification to the second embodiment. In this ink storagetank 1301, two air communication ports 1309 are formed one each in ahigher wall section 1302 a 1 and a lower wall section 1302 a 2 of a topwall 1302 a of a tank body 1302, as in the third modification to thefirst embodiment illustrated in FIG. 6. Alternatively, only one aircommunication port 1309 may be formed in one of the higher wall section1302 a 1 and the lower wall section 1302 a 2 of the top wall 1302 a.

FIG. 16 illustrates a replenishing-type ink storage tank 1401 accordingto an eighth modification to the second embodiment. Similar to thefourth modification to the first embodiment illustrated in FIG. 7, thepartitioning wall 4 is not provided in a tank body 1402 of the inkstorage tank 1401. A backpressure application member 1403 isaccommodated in the tank body 1402 to extend across the absorberaccommodating portion 6 and the ink storage portion 5. Specifically, thebackpressure application member 1403 has a stepped configuration as inthe backpressure application member 403 of FIG. 7. That is, thebackpressure application member 1403 has a portion having a higher levelend 1403 a 1; and another portion having a lower level end 1403 a 2lower than the higher level end 1403 a 1. The portion having the higherlevel end 1403 a 1 is accommodated in the absorber accommodating portion6, and the portion having the lower level end 1403 a 2 is accommodatedin the ink storage portion 5. The functional lower limit indicator ML1is at a height equal to or higher than a lower end of the entirebackpressure application member 1403. That is, the auxiliary absorber 7of the second embodiment is not provided in the tank body 1402. Further,the ink inlet port 8 is positioned to be in separation from the lowerlevel end 1403 a 2 of the backpressure application member 1403.

Incidentally, in the ink storage tank 1401, the air communication port 9may be provided in the higher wall section 2 a 1 of the top wall 2 a,rather than in the lower wall section 2 a 2 of the top wall 2 a. In theink storage tank 1401 without the partitioning wall 4, the aircommunication port 9 is preferably formed in the higher wall section 2 a1 rather than in the lower wall section 2 a 2. However, the ink storagetank 501 including the partitioning wall 4 and having the aircommunication port 9 formed in the lower wall section 2 a 2 is mostpreferable.

Still further, while the backpressure application member 3 of the firstand second embodiments is a one-piece component, the backpressureapplication member 3 may be provided by aggregation of a plurality ofbackpressure applying blocks. In the latter case, the backpressureapplying blocks may have liquid absorbing performance different from oneanother in order to adjust liquid absorbing performance, i.e.,backpressure application performance of the aggregated blocks.Particularly, the plurality of backpressure applying blocks may bestacked one after another so that the liquid absorbing performance of alower block is higher than that of a higher block, i.e., the liquidabsorbing performance of the higher block is lower than that of thelower block. With this structure, the backpressure application member 3as a whole (aggregated blocks) has an upper portion where liquidabsorbing performance is relatively lower, preventing the absorbed inkfrom spreading to the backpressure application member 3 in its entirety.Hence, the backpressure application function of the overall backpressureapplication member 3 is prevented from being lowered or vanished.

The above-described embodiments and modifications thereto may becombined with one another, as appropriate, in order to obtain the sametechnical and operational advantages.

While the description has been made in detail with reference to thespecific embodiment, it would be apparent to those skilled in the artthat various changes and modifications may be made therein withoutdeparting from the scope of the above described embodiment.

<Remarks>

The ink storage tanks 1, 301, 401, 501, 601, 701, 801, 901, 1101, 1201,1301 and 1401 are examples of a replenishing-type liquid storage tank.The tank bodies 2, 302, 402, 502, 602, 702, 802, 902, 1102, 1202, 1302and 1402 are examples of a tank body. The backpressure applicationmembers 3, 3A-3C, 403 and 1403 are examples of a backpressureapplication member. The auxiliary absorbers 7, 707, 807, 907, 1107 and1207 are examples of an auxiliary absorber. The ink inlet ports 8 and108 are examples of a liquid inlet port. The ink outlet ports 10, 710,810, 910, 1110 and 1210 are examples of a liquid outlet port. Thepartitioning wall 4 is an example of a partitioning wall. The inkstorage portion 5 is an example of a liquid storage portion. Theabsorber accommodating portion 6 is an example of an absorberaccommodating portion. The upper limit indicator UL (rib 2L) is anexample of an upper limit indicator. The functional lower limitindicator ML1 is an example of a functional lower limit indicator. Thevisual lower limit indicator ML2 (ribs 502L, 602L) is an example of avisual lower limit indicator. The control lower limit indicator ML3 isan example of a control lower limit indicator.

What is claimed is:
 1. A replenishing-type liquid storage tankcomprising: a tank body in which liquid is replenishable and configuredto store the liquid therein; and a backpressure application memberaccommodated in the tank body to apply backpressure to the liquid storedin the tank body, wherein the backpressure application member has alower end positioned at a height equal to or lower than a liquid levelof a minimum amount of liquid required to be stored in the tank body forenabling the backpressure application member to apply backpressure tothe liquid stored in the tank body.
 2. The replenishing-type liquidstorage tank according to claim 1, wherein the backpressure applicationmember is made from a material capable of absorbing liquid.
 3. Thereplenishing-type liquid storage tank according to claim 1, furthercomprising a functional lower limit indicator set in the tank body, thefunctional lower limit indicator being indicative of the liquid level ofthe minimum amount of liquid required to be stored in the tank body. 4.The replenishing-type liquid storage tank according to claim 1, furthercomprising a visual lower limit indicator set in the tank body andindicative of a lowermost liquid level of the liquid stored in the tankbody subject to user's visual inspection, wherein the liquid level ofthe minimum amount is lower than the visual lower limit indicator. 5.The replenishing-type liquid storage tank according to claim 4, furthercomprising a partitioning wall partitioning an internal space of thetank body into a liquid storage portion configured to store the liquidand an absorber accommodating portion in which the backpressureapplication member is accommodated, the partitioning wall having a lowerend, wherein the liquid storage portion and the absorber accommodatingportion are allowed to communicate with each other at a height lowerthan the visual lower limit indicator, and wherein the liquid level ofthe minimum amount is at a height equal to or higher than the lower endof the partitioning wall.
 6. The replenishing-type liquid storage tankaccording to claim 1, further comprising: a control lower limitindicator set in the tank body and indicative of a lowermost liquidlevel of the liquid stored in the tank body subject to a residual amountdetection based on an ejected amount of the liquid, wherein the liquidlevel of the minimum amount is lower than the control lower limitindicator.
 7. The replenishing-type liquid storage tank according toclaim 1, wherein the tank body comprises a liquid outlet port throughwhich the liquid is allowed to flow out of the tank body after passingthrough the backpressure application member.
 8. The replenishing-typeliquid storage tank according to according to claim 1, furthercomprising an auxiliary absorber disposed in the tank body andconfigured to absorb the liquid stored in the tank body, the auxiliaryabsorber being positioned below the backpressure application member andin contact with the backpressure application member.
 9. Thereplenishing-type liquid storage tank according to claim 8, wherein thetank body comprises a liquid outlet port through which the liquid isallowed to flow out of the tank body, and wherein the liquid isconfigured to be discharged through the liquid outlet port after passingthrough at least one of the auxiliary absorber and the backpressureapplication member.
 10. The replenishing-type liquid storage tankaccording to claim 9, wherein the liquid outlet port has a surfacefacing the auxiliary absorber, the surface having a part in contact withthe auxiliary absorber.
 11. The replenishing-type liquid storage tankaccording to claim 9, wherein the liquid outlet port has a surfacefacing the auxiliary absorber, an entirety of the surface being incontact with the auxiliary absorber.
 12. The replenishing-type liquidstorage tank according to claim 9, wherein the liquid outlet port has asurface facing the auxiliary absorber, the surface being separated fromthe auxiliary absorber.
 13. The replenishing-type liquid storage tankaccording to claim 8, further comprising a partitioning wallpartitioning an internal space of the tank body into a liquid storageportion configured to store the liquid and an absorber accommodatingportion in which the backpressure application member is accommodated,wherein the liquid storage portion and the absorber accommodatingportion are in communication with each other through a gap, and whereinthe auxiliary absorber extends through the gap to span across the liquidstorage portion and the absorber accommodating portion.
 14. Animage-forming apparatus comprising: the replenishing-type liquid storagetank according to claim 1; and a recording head configured to form animage on an image recording medium with the liquid supplied from thereplenishing-type liquid storage tank.